Mind-Controlling Parasites Date Back Millions of Years

A parasitic fungus stalk erupted from the head of a dead carpenter ant whose jaws are gripping the underside of a leaf's major vein. (David Hughes)

Mind control by parasite sounds like the stuff of science fiction, but not only have scientists revealed that it is real across a range of animals -- including perhaps humans -- they now even have fossil evidence suggesting it has taken place for millions of years.

An unnerving variety of parasites have evolved the ability to control the brains of victims to help the parasites spread. For instance, the protozoan known as Toxoplasma gondii makes rats love cat urine so that it can spread among its feline hosts -- and it may influence human culture as well, making people more prone to certain forms of neuroticism.

Another case of parasite mind control involves the fungus Ophiocordyceps unilateralis, which essentially turns ants into zombies. It maneuvers the insects into biting down on the major veins of the undersides of leaves just before they die -- the fungus then rapidly grows a stalk from their victims' heads, releasing spores to infect more ants.

Now scientists have discovered what might be ancient evidence of such mind-control-induced death grips -- scars on a roughly 48-million-year-old leaf.

"I thought it was a very, very long shot to find such a fossil, but indeed, as luck would have it, two paleobotanists, Conrad Labandeira at the Smithsonian Institution in Washington and Torsten Wappler at the Steinmann Institute in Bonn, were sitting around wondering how that particular damage type might be explained," said researcher David Hughes, a behavioral ecologist at Harvard University.

The leaf fossil came from what once were subtropical forests around a lake in Germany. The leaf bears 29 dumbbell-shaped scars centered around its veins. These differ from the kinds of snips resulting when insects drink plant sap, and match telltale scars made nowadays by the death grips of carpenter ants (Camponotus leonardi) infected with the mind-controlling fungus O. unilateralis.

"We are now realizing that half of life on Earth is parasitic -- each free-living organism has at least one parasite," Hughes said. "But very few manipulate behaviors and there is a reason for that -- it is likely very costly. The fossil now challenges us to think of what past environments acted as selective forces for such cool tricks to evolve."

Hughes, Labandeira and Wappler detailed their findings online Aug. 18 in the journal Biology Letters.

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